tesla powerwall case study

Case study: Tesla Powerwall installation with Green Mountain Power in Vermont

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EnergySage’s own vice president of marketing, Luke Tarbi, just had a Tesla Powerwall 2 installed at his home in Vermont through Green Mountain Power’s new program – for just $15/month! In this case study, he shares his experience with the program.

We’d just closed on the house in Southern Vermont. Fortunately, the sellers left the house mostly furnished and stocked with supplies and a helpful “home instructions” booklet. One line of their “home instructions” stood out to us: “In the event of a power outage, there are flashlights and candles in the mudroom.”

One of the downsides of living in a heavily wooded area like the Green Mountain National Forest is that we’re susceptible to the occasional power outage due to storms and downed wires. This is particularly a risk in Vermont’s long winter months, when the tree limbs are heavy with snow and ice, and a strong wind can bring them down atop power lines.

Signing up with Green Mountain Power for a Tesla Powerwall

In May 2017, Green Mountain Power (our soon-to-be utility, also known as GMP) announced an innovative new partnership with Tesla. For $15 per month, we could add a new Tesla Powerwall 2 battery to our home.

In addition to backup power benefits, we would also contribute to GMP’s efforts to rely on distributed energy storage – instead of natural gas “peaker plants” – to meet spikes in electricity demand. We were determined to support the pilot program, which the New York Times described as “a bold experiment aimed at turning homes, neighborhoods and towns into virtual power plants, able to reduce the amount of energy they draw from the central electric system.”

$15 per month seemed like a great deal given the resiliency benefits and positive environmental impact. As a point of comparison, buying and installing the Tesla Powerwall 2 outright would cost over $10,000. Leasing it from Green Mountain Power will cost us just $180 per year, or $1,800 over the 10-year term. (We also had the option to pay for the 10-year lease upfront at a slight discount of $1,500).

In early June, I contacted Green Mountain Power and asked if we could join their pilot program. A few hours later, I received this welcome email (below) and a verbal confirmation that we were in fact one of the first several hundred customers enrolled in their 2,000-household pilot program.

This ended up being our last communication I received from Green Mountain Power – all messages and calls from that point forward were with Tesla Energy.

Scheduling with Tesla and installation preparation

In early November 2017, about five months after receiving the welcome email from Green Mountain Power,­ I received an email from an Energy Advisor at Tesla. We scheduled a call to discuss the Powerwall 2 pilot program in more detail.

Tesla’s Energy Advisors were based out of Las Vegas. They were my main point of contact for the scheduling process, and were knowledgeable and fun to talk to. From what I could tell, they had a few goals:

  • Confirm whether I already had solar panels or planned to install them
  • Verify that I understood the structure of the leasing arrangement with my utility (10 years at $15 per month)
  • Verify that I understood that Green Mountain Power could use the energy stored Powerwall during peak energy times, so long as we weren’t relying on it at that moment.

Before signing the lease contract with Green Mountain Power, I had to take the Tesla Powerwall Self-Survey to identify the location of the requested battery installation, share photos of my electric panel, and discuss any unique electrical requirements (our hot tub is on a separate breaker, for example). The self-survey process required a smartphone and Internet connection, took about 30 minutes, and was intuitive and easy to complete. Everything was done remotely, though Tesla offered to send out a representative if had I requested it.

After emailing the self-survey back to Tesla’s Energy Advisors, their engineers remotely designed a blueprint of the project. This design process took about three weeks from start to finish. Before I could schedule the actual installation date, Tesla sent me a contract and installation design to review via email.

Contracting with Tesla and Green Mountain Power 

In early January 2018, Tesla sent me the final leasing contract and installation project design. The most interesting part of the contract to me was the description of the utility’s use of the energy from my soon-to-be battery:

“Customers participating in the Grid Transformation Innovative Pilot (the “Pilot”) will lease a Tesla Powerwall 2 and Tesla gateway (the “Devices”), and both will be installed in their Home by Tesla or authorized Tesla contractors or subcontractors. The Powerwall will provide Customer with backup power during a Grid outage. Duration of backup power will depend on the amount of energy stored in the Powerwall at the time of outage. The Grid Transformation Pilot also provides Green Mountain Power with the ability to access the Powerwall for the purpose of reducing energy costs during peak energy periods.”

After I signed the contract, Tesla’s Energy Advisor reviewed it and then scheduled an installation date for the following month, February 2018.

Installation day with Tesla

The three-person team from Tesla Energy arrived at 10:00 am on a Friday in mid-February. All three were former SolarCity employees and had experience with solar panels as well as battery storage. They were all friendly, professional, and wore matching black hoodies with Tesla emblazoned on the front.

We walked the exterior and interior of the house after their arrival to identify the best location to install the Tesla Powerwall 2. The Tesla Powerwall 2 will technically perform better in an indoor environment due to less extreme changes in temperature, but it can also be installed outside. Ideally it would be installed within 20 feet of the electric meter, but further is possible. When located outdoors, the battery should be placed in a more protected area if possible.

Tesla’s remote design team in Las Vegas had initially thought an indoor installation was possible in our mudroom, but the onsite team didn’t concur – they thought it would take up too much space and limit our mudroom’s storage potential (pun intended!!). I agreed with them, and we opted for an outdoor installation under the eave of our roof in a dry location with good sun exposure.

The installation process took about six hours in total, the latter four of which had to have the power turned off. The newly installed battery can provide backup power for all our electric appliances under 30 Amp.

The Powerwall can’t back up devices over 50 Amp (this is called a “partial home backup”). As a result, we had to move our electric stove and hot tub to a new electric panel on the exterior of the house. The panel is between the electric meter and the battery so that the Tesla Powerwall can supply backup power to all of our critical appliances on the interior panel (electric baseboard heating, lighting, refrigerator, etc.) but will not attempt to power our stove or hot tub in a power outage.

Our Tesla Powerwall 2, installed on the south side of the house.

As an added benefit, moving the stove and hot tub breakers to a new electric panel created additional space in our original electric panel for future electrical appliances. In our case, we’re planning to add an air source heat pump (ASHP) in the next few months. This new breaker space will allow the ASHP to be backed up by the Tesla Powerwall battery in cases of power outages, ensuring we have access to an energy-efficient heating source even in storms and blackouts.

Closing thoughts on Green Mountain Power and Tesla

Overall, I’ve been impressed with the responsiveness and professionalism of both Green Mountain Power and Tesla Energy, especially given the fact that this is a pilot program for both of them, and our home was one of its first participants.

I’m pleased that Green Mountain Power is taking a proactive role in ensuring we have access to reliable backup power in case of emergency, all at the bargain price of $15 per month. I’m also optimistic about this pilot program more broadly, and hope that it can serve as a model for larger utilities to study – particularly in parts of the U.S. where other homeowners are similarly worried about blackouts and grid reliability.

I’ve also been impressed with Tesla Energy’s customer support, installation crew, and use of online and mobile technology wherever possible (screenshots below). The Tesla mobile app allows us to monitor how charged our battery is, and watch the flow of power from the grid to our battery and our Vermont cabin.

The “charging” status in the Tesla Powerwall app.

When the power is out and our home is fully relying on the battery, the app puts a big X over the “grid” icon so it’s completely apparent that we’ve really “gone off grid.”

Tesla Energy’s installers worked with me to free up space in my electric panel, setting us up for the installation of an ASHP down the road – all at no marginal cost to me, and no real benefit to Tesla (as they don’t yet sell air source heat pumps!). Overall, it was a great experience to work with both Green Mountain Power and Tesla Energy, and we’re excited to be part of this new pilot program in Vermont.

Any questions for me? Ask them in the comments section below.

Update July 2018: Green Mountain Power’s “virtual power plant” springs into action

Our Powerwall went into overdrive in the first week of July during the heatwave, as Green Mountain Power was pulling power rapidly from its 500+ batteries across the state to meet surges in electricity demand. Here’s what my energy usage report looked like on my Tesla app:

My energy usage overview for the week of the July heatwave in the Tesla app

Even though I wasn’t at the house during most of the week, the app showed stored battery power being pulled back to the grid every day (see the green bars below the axis). You can see that they needed so much power that by Sunday, my battery was completely drained. They had to refill it again on Monday, then used a lot of it to meet spiking demand on Tuesday and Wednesday. GMP wrote a great article about this heat wave, and explained that “during the hours of peak demand, this [virtual power plant] helped GMP offset approximately 17,600 pounds of carbon, the equivalent of not using about 910 gallons of gasoline.”

23 thoughts on “Case study: Tesla Powerwall installation with Green Mountain Power in Vermont

  1. Terry

    Looking at the spec sheet I see it has a 10 year warranty. Not sure how that $10,000 – $18,000 investment compares to purchasing a generator to meet the same needs during a power outage.

  2. Barry Smith

    Hello. Thank you for your post! Can you please tell me, is it possible to “milk” the power from your battery slowly so that it lasts longer than a single day? For ex., we lost power for a week or so last winter. I would like to be able to heat the house, run the fridge, etc., “just enough” to keep things in good shape, so food doesn’t spoil, pipes don’t freeze, etc. So – if I could just run off the battery for an hour or so a couple of times during the night, that would seem more useful. Is that possible?

  3. rjns

    Luke, how well is your PW holding up being in freezing outdoor temps? We want to install grid-tied PV with battery for new mountain cabin in CA at 5200 ft elevation. Two outages this year so far due to high winds and fire, 4 to 5 days each. Gets to about 20F in winter at night.

    I’m also having difficulty finding a solar contractor that will work with me to design a system for a house we’re designing right now. According to an Energy Sage rep, the contractors only work on existing homes. I find this hard to believe that no one can incorporate solar design into an overall house design so placement and wiring can all be accounted for before construction starts.

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